The present invention relates to improvements in gravity ore separators and is particularly directed to the efficient separation of valuable metals from an aggregate ore containing a relatively small percentage thereof.
Comparable known prior art separators, such as that disclosed by Katter U.S. Pat. No. 3,815,737, generally move metal-bearing aggregate ore across a perforate member so as to permit small particles or fines to fall into a classifying chamber where they are compacted into layers according to density with the heavier fines in the lowermost layers. Once compaction is achieved, the fines are advanced upwardly, by a first rotating helix formed in the bottom surface of the classifying chamber, through a shaving area, and toward an outlet. The shaving area includes a second rotating helix protruding downwardly by a predetermined distance into the classifying chamber and arranged so as to move the upper layers of the fines in a direction opposite to that of the first helix. The second helix functions to shave off the upper layers of the fines, so that only a predetermined quantity of the heaviest fines--the desired concentrates--are conveyed by the first helix to the outlet. These concentrates can then be transported to a distant plant for processing.
Several difficulties attend this form of classification and have heretofore precluded efficient high-percentage recovery. A major difficulty with mechanical classifiers of the type described is that the shaving action is governed by physical dimensions of the mechanical shaver, rather than by the density of the fines, and is therefore not readily adjustable to compensate for aggregate ores of varying densities. Such a shaving action being unable to differentiate between high- and low-grade aggregate produces a concentrate that varies in quality essentially as the quality of the aggregate varies. The provision of the complex machinery necessary to vary the action of the mechanical shaver according to the density of the aggregate would increase the cost and complexity of the classifier considerably.
Another deficiency of known comparable mechanical separator/classifiers is that aggregate conglomerates moving through the system tend to bridge the perforations of the perforate member and inhibit the passage of fines into the classifying assembly. Some mechanical classifiers provide water flow apparatus in order to decrease this clogging of the classifier; however, the action of the water is usually such as to interfere with the shaving action of the apparatus and thereby lower its overall efficiency.
Still another deficiency of known mechanical classifier/separators is their inability to separate large metal-bearing particles from similarly large gravel particles without requiring the apparatus to be periodically stopped to permit the large metal-bearing particles or nuggets to be removed by hand.
Known aggregate ore processing equipment has also failed to adequately resolve the competing considerations of accuracy, cost, capacity and portability. A major portion of valuable metal resources are located at numerous diverse locations in relatively modest amounts. Economical use of these resources inherently demands an apparatus which can collect concentrates with a certain level of accuracy from these diverse locations for collective processing at a distant smelter plant. The modest amount of valuable metal relative to total aggregate ore at each remote site inherently demands an inexpensive large volume classifier which is readily transportable, requires a minimum set-up time and is virtually self-sustained. Conversely, the relative scarcity of the valuable metals demands an optimization of classifying accuracy. Known classifying systems have failed to resolve these competing considerations and have heretofore denied the industry access to small-scale ore deposits which collectively comprise large quantities of the valuable metal.
What is needed therefore, and what is provided by the present invention, is an ore classifier of the mechanical separator type which can achieve inherently high percentage recovery of valuable metal from low-grade aggregate ore through the use of a shaver-classifier mechanism of simple and uncomplex design which differentiates among particles according to the density thereof without resulting in any significant lowering of the system through-put efficiency and which is readily transportable to a remote site, efficiently placed in operation, and requires minimal support facilities.